The present invention relates to systems for automatically controlling the speed of a vehicle and, more particularly, to systems for automatically limiting speed of a vehicle in response to external signals.
The crowding of highways, the need for conservation of full, and increasing concern for safety, have emphasized the importance and desirability of rigidly enforcing the observation of vehicle speed limits in general.
Moreover, there has been a long-felt need to provide a way of ensuring that drivers of vehicles observe reduced speed limits in situations or locations where their operation of vehicles in excess of speed limits constitutes a clear and present danger to themselves, occupants of other vehicles, or pedestrians. Operation of vehicles in conditions of reduced visibility, in crowded municipalities, or in school zones, mandates reduced speeds. Yet, safety statistics illustrate that voluntary compliance with posted speed limits is often unsatisfactory in such situations.
Accordingly, it is believed desirable to be able to automatically limit vehicular speed under certain circumstances. Many proposals have been made heretofore for systems which limit speed. For example, Huebscher U.S. Pat. No. 2,070,432 discloses a system for controlling the speed of a vehicle in which the driver is constantly advised by colored lights or marks of the maximum speed he is permitted to travel in a given zone. This Patent also discloses that a governor on the vehicle may then be set by the operator to maintain a speed according to the colored code. This system requires the voluntary cooperation of the driver.
Ferrill U.S. Pat. No. 2,493,755 describes a system for vehicle speed control involving photoelectric sensing of a continuous series of reflective speed control strips embedded in a pavement. This system requires the continuous periodic presence of such strips for speed control purposes since the spacing between strips establishes the speed limit.
Sampey U.S. Pat. No. 3,642,087 is another disclosure of a system for maintaining vehicle speed in response to photoelectric detection. Similarly, this system controls speed in accordance with the spacing between reflective pavement elements and also requires the continuous periodic presence of such strips for speed control to be maintained. A similar concept is taught by Lambert U.S. Pat. No. 3,353,619.
There have been numerous other disclosures of speed control systems using either passive or active transmission of radiant energy to a vehicle for the purpose of controlling its speed or alerting a driver to a speed limit. The prior art "active" systems (where a transmitter beams some form of radiant energy to signify a speed zone) there are inherent disadvantages, such as high cost of installation, complexity, and need for costly maintenance. In prior art "passive" systems (where spaced passive reflective, magnetic, or radioactive elements are detected by apparatus carried by a vehicle) disadvantages include high costs of installation and maintenance due to large numbers of elements. Another disadvantage is the difficulty of changing the speed limit in a zone, again resulting from the use of large numbers of elements or the requirement that they have a predetermined spacing.